The present invention relates to highly active catalysts for olefin metathesis reactions, and the preparation of the catalysts. The invention also relates to the olefin metathesis reactions catalyzed with the catalysts of the invention.
The past several years have witnessed a healthy surge in catalyst development related to metathesis reactions of olefins, in particular metathesis polymerization of olefins. These well defined catalysts usually possess a metal-carbon double bond (metal-carbene or alkylidene) that can coordinate to the alkene moiety of the olefin, and in particular, can perform the ring opening of cyclo-olefin monomers in a rather facile manner. Most of the metals that exhibit remarkable activity for this phenomenon are second-or third-row mid-to late- transition metals. Although the specific reason for this observation has not been clearly articulated, many theories have been proposed, the most prevalent of which is that late transition metals exhibit greater robustness towards the impurities that may inherently be present within a reaction system and, consequently, catalysts containing those metals resist degradation.
Among olefins, cyclo-olefin monomers like norbornene (NB) or dicyclopendadiene (DCPD) which possess a strained double bond can readily undergo ring opening metathesis polymerization (ROMP) because the ring opened product is thermodynamically favored. For ring opening to occur in these cyclo-olefins there is no pre-requisite for the catalyst to possess a metal-carbene moiety in its framework, because any organometallic complex that has the capability of initiating a metal-carbene formation in situ can also perform as a catalyst. For instance, it is well known that RuCl3.3H2O can accomplish the ROMP of NB quite effortlessly, even though there is no carbene present in the catalyst. It is hypothesized that the first step of the reaction, when the metal halide reacts with the monomer, is the formation of a metal carbene moiety that is responsible for further polymer propagation.
The catalysts that have received the greatest exposure in the literature by far are those designed by Schrock et al., as reported in Schrock et al., J. Am. Chem. Soc., 1990, 112, 3875, and by Grubbs""s group, as reported in Fu et al., J. Am. Chem. Soc., 1993, 115, 9856; Nguyen et al., J. Am. Chem. Soc., 1992, 114, 3974; and Grubbs et al., WO98/21214 (1998). The Grubbs catalyst (a ruthenium carbene) is slightly more versatile than the Schrock catalyst (a molybdenum alkylidene) because of its ease of synthesis as well as its utility from a commercial viewpoint. Cox and co-workers reported in Cox et al., Inorg. Chem., 1990, 29, 1360; Cox, et al., J. Chem. Soc., Chem. Commun., 1988, 951-953; and Porri et al, Tetrahedron Letters, No. 47., 1965, 4187-4189, the synthesis of a class of metal catalysts based on ruthenium metal. These catalysts consist primarily of a bis-allyl ligand wrapping the metal, along with two or three acetonitrile ligands. Additionally, these catalysts possess a mono- or di-anion that is virtually (i.e., almost) coordinated to the metal center, which is therefore considered to be formally in the +4 oxidation state. These complexes in conjunction with diazo ethyl acetate have been used by Herrmann""s group, as reported in Herrmann et al., Angew. Chem. Int""l. Ed. Engl., 1996, 35, 1087, to investigate the polymerization (specifically the ROMP) of NB. Herrmann has conjectured that the active species in the catalyst system is a metal carbene generated in situ when the ruthenium reacts with the diazo alkyl compound (such as diazo ethyl acetate).
A disadvantage of the above catalysts is that for the ROMP of cyclic olefins these catalysts must be used with a co-catalyst such as a diazo alkyl compound, which requires special caution in handling because of the instability of the diazo group.
One aspect of the invention is to provide catalysts which are highly active in initiating metathesis reactions in olefins.
Another aspect of the invention is to provide catalysts which are highly active in the ring-opening polymerization (ROMP) of cyclo-olefin monomers without requiring the presence of a co-catalyst such as a diazo alkyl compound.
Another aspect of the invention is to provide methods for the preparation in good yield of the catalysts for metathesis reactions in olefins.
Yet another aspect of the invention is to provide a highly effective method for polymerizing olefins, in particular cyclo-olefins, using the catalysts of the invention.
The catalysts of the invention are characterized by a complex cation represented by the formula I*, II* or III* below, wherein the ruthenium atom is in the 4+ oxidation state, has an electron count of 14, and is penta-coordinated. 
wherein
each of X1 and X2, which may be the same or different, is a C3-C20 hydrocarbon group having an allyl moiety as an end group bonded to the ruthenium atom, optionally substituted with a C1-C20 alkyl, a C1-C20 alkoxy, or a C6-C12 aryl group on its backbone, said allyl moiety optionally having up to three functional groups independently selected from the group consisting of hydroxyl, thiol, thioether, ketone, aldehyde, ester, ether, amine, imine, amide, nitro, carboxylic acid, disulfide, carbonate, isocyanate, carbodiimide, carboalkoxy, carbamate, and halogen; or
X1 and X2 together form a group which results from dimerization of an alkene and has at each end an allyl group bonded to the ruthenium atom, said group resulting from the alkene dimerization being optionally substituted on its backbone with a C1-C20 alkyl, a C1-C20 alkoxy, or a C6-C12 aryl group, and further optionally having a functional group selected from the group consisting of hydroxyl, thiol, thioether, ketone, aldehyde, ester, ether, amine, imine, amide, nitro, carboxylic acid, disulfide, carbonate, isocyanate, carbodiimide, carboalkoxy, carbamate, and halogen;
L1 and L2, which may be the same or different, are monodentate neutral electron donor ligands;
L3 is a solvent molecule coordinated to the central ruthenium atom or a neutral monodentate electron donor ligand;
L{circumflex over ( )}L is a bidentate neutral electron donor ligand; and
L{circumflex over ( )}L{circumflex over ( )}L is a neutral tridentate electron donor ligand.
More specifically, the catalysts of the invention are cationic complexes represented by the formula I, II or III below, wherein the ruthenium complex cation is paired with a counter anion A. 
wherein X1, X2, L1, L2, L3, L{circumflex over ( )}L and L{circumflex over ( )}L{circumflex over ( )}L are as described above, and A is a counter anion which is weakly coordinated to the central ruthenium atom in the complex cation.
The neutral electron donor ligand as recited in the definition of L1, L2, L3, L{circumflex over ( )}L and L{circumflex over ( )}L{circumflex over ( )}L in the complex cations of the invention is any ligand which, when removed from the central ruthenium atom in its closed shell configuration, has a neutral charge, i.e., is a Lewis base. Preferably, at least one of the monodentate neutral electron donor ligands in the complex cation is a sterically encumbered ligand. Examples of sterically encumbered monodentate ligands are phosphines, sulfonated phosphines, phosphites, phosphinites, phosphonites, arsines, stibines, ethers, amines, amides, imines, sulfoxides, carboxyls, nitrosyls, pyridines, and thioethers.
In a preferred embodiment, each of X1 and X2, which may be the same or different, is a C3-C20 hydrocarbon chain with an allyl moiety as an end group bonded to the ruthenium atom. The hydrocarbon chain may be substituted on its backbone with up to three substituents independently selected from C1-C20 alkyl, C1-C20 alkoxy, and C6-C12 aryl groups. The allyl moiety may further have up to three functional groups independently selected from: hydroxyl, thiol, thioether, ketone, aldehyde, ester, ether, amine, imine, amide, nitro, carboxylic acid, disulfide, carbonate, isocyanate, carbodiimide, carboalkoxy, carbamate, and halogen.
In another preferred embodiment, X1 and X2 together constitute the group resulting from the dimerization of an alkene, for example isoprene, said group resulting from the dimerization of an alkene optionally having on its backbone up to three substituents as described above, and further optionally having up to three functional groups as described above.
In a preferred embodiment, L1 and L2, which may be the same or different, are selected from phosphines, sulfonated phosphines, phosphites, phosphinites, phosphonites, arsines, stibines, ethers, amines, amides, imines, sulfoxides, carboxyls, nitrosyls, pyridines, and thioethers. In a more preferred embodiment, L1 and L2, which may be the same or different, are phosphines of the formula PR1R2R3, wherein R1 is a C3-C12 secondary alkyl or a C5-C12 cycloalkyl group, and R2 and R3 are independently selected from the group consisting of a C6-C12 aryl, a C1-C10 primary alkyl, a C3-C12 secondary alkyl and a C5-C12 cycloalkyl. In a most preferred embodiment, L1 and L2, which may be the same or different, are P(cyclohexyl)3, P(cyclopentyl)3, P(isopropyl)3, or P(t-butyl)3.
In another embodiment, L1 and L2, which may be the same or different, are amines represented by the formula NR1R2R3, wherein R1 is a C3-C12 secondary alkyl or a C5-C12 cycloalkyl group, and R2 and R3 are independently selected from the group consisting of a C6-C12 aryl, a C1-C10 primary alkyl, a C3-C12 secondary alkyl and a C5-C12 cycloalkyl. In such a preferred embodiment, L1 and L3, which may be the same or different, are N(ethyl)3 or N(methyl)3.
L1 and L2 taken together may also be a bidentate ligand coordinated to the central ruthenium atom through phosphorus, nitrogen, arsenic atoms or a combination thereof. The bidentate ligand preferably has up to 30 carbon atoms and up to 10 heteroatoms selected from phosphorus, nitrogen and arsenic. Examples of the bidentate ligand are 1,2-bis(diphenyl-phosphino)ethane, 1,2-bis(diphenylarsino)ethane, bis(diphenylphosphino)methane, ethylenediamine, propylenediamine, propylenediamine, diethylenediamine, arphos (i.e., arsine phosphine), phen (i.e., phenanthroline), bpy (i.e., bipyridine), and xcex1 di-imine. In such embodiment having a bidentate ligand, the L3 ligand preferably is a solvent molecule, as described above, which may have an oxygen, nitrogen, sulfur, or selenium atom coordinating to the central ruthenium atom.
The L1, L2 and L3 groups taken together may also be a tridentate ligand derived from phosphorus or nitrogen. An example of a suitable tridentate ligand is triphos.
In embodiments of the catalysts of the invention wherein L3 is a solvent molecule, the solvent preferably is selected from THF, acetonitrile, pyridine, triethyl amine, and a thiol.
The anion A that is very weakly coordinated to the metal center may be derived from any tetra coordinated boron, such as BF4xe2x88x92, or hexa coordinated phosphorus, such as PF6xe2x88x92. The weakly coordinated anion A may also be any one of the following: ClO4xe2x88x92; fluorinated derivatives of BPh4xe2x88x92 such as B(C6F5)4xe2x88x92, Ph3BCNBPh3xe2x88x92, carba-closo-dodecaborate (CB11H12xe2x88x92) and other carboranes, pentafluorooxotellurate (OTeF5xe2x88x92); HC(SO2CF3)2xe2x88x92; C60xe2x88x92; B(o-C6H4O2)2xe2x88x92; H(1,8-BMe2)2C10H6xe2x88x92; or any of the anionic methylaluminoxanes.
Examples of preferred catalysts according to the invention are: 
The catalysts of the invention may be prepared starting from allyl dimer complexes represented by the formula [(X1)(X2)RuY2] shown below, wherein X1 and X2 are allyl-containing groups as described above, and Y is a halide, for example chloride. A suitable allyl ruthenium dimer complex is [(allyl)RuCl2] wherein the allyl group is the 2,7 dimethyl-octadiene-diyl ligand, which may be prepared from isoprene and commercially available ruthenium (III) chloride, for example by the method disclosed in Schlund et al., J. Am. Chem. Soc., 1989, 111, p. 8004. 
The two reactions schemes shown below may be followed for the synthesis of the complexes of the invention. Of those two methods, the simple one-pot method (Reaction Scheme B) may be used for preparing all the ruthenium catalysts of the invention from an [(X1)(X2)RuY2]2 dimer. Both processes result in good product yield without the need for expensive and sophisticated equipment. Furthermore, the methods can produce catalysts in a form which does not require post purification of the synthesized materials.
The one-pot synthesis is particularly convenient because the catalysts of the invention can be prepared by simply adding the appropriate reagents sequentially in stoichiometric quantities. Both procedures do not require the stringent methodologies typical of organometallic syntheses, and the formation of most of the complexes of the invention can be accomplished within a few hours in both procedures. Post purification of the isolated complexes is usually not required, and since the yield of these catalysts is typically greater than 90%, both synthesis methods are commercially viable.
The catalysts of the invention are synthesized by using a solvent that can favorably coordinate and occupy one of the coordination sites on the ruthenium atom. The solvent is required for maintaining the coordination geometry prior to the metathesis reaction, for example polymerization, but should dissociate quickly in the presence of the olefin, for example an olefin monomer being polymerized. In this regard, solvents with oxygen and nitrogen donors are preferred since they can dissociate easily in the presence of the olefin, and provide a vacant site for the olefin to coordinate to the central ruthenium atom.
General Synthetic Schemes
The ruthenium catalysts may be synthesized according to the reactions schemes described above, using readily available stable starting materials. In general, the formation of complexes of the invention can be completed in a few hours, and the percent yield obtained in most cases is good to excellent, typically greater than 80%. The reactions are sufficiently clean with practically no side or competing reactions occurring simultaneously. These preparations generally may be carried out at room temperature with minimum constraints. The general synthetic schemes are illustrated below for embodiments of the complexes represented by formula I, II and III. 
In a preferred embodiment of the catalyst represented by formula (I) above, L1 and L2 are tricyclohexyl phosphine, which are highly sterically encumbered neutral donor electron ligands; L3 is THF which is a solvent capable of coordinating with the ruthenium central atom and is also a neutral donor ligand; X1 and X2 are the bidentate 2,7 dimethyl-octadiene-diyl ligand; and A is the BF4xe2x88x92 anion. The formation of this catalyst can be accomplished by contacting a ruthenium dimer complex as shown above (wherein M=Ru; X1 and X2 are the bidentate 2,7-dimethyl-octadiene-diyl ligand, and Y is the Cl ligand) with THF, a solvent that is capable of coordinating to the central ruthenium atom. To the resultant product a compound of the formula B+Axe2x88x92 is added to precipitate out the chloride salt. For example, AgBF4 is used as the salt to precipitate out AgCl from the reaction. Finally, the neutral electron donor ligands L1 and L2 (for example, tricycloalkylphosphines) are added to the reaction system, and the complex catalyst is recovered as a product of the reaction.
In another aspect of the present invention, a solvent wherein the donor atom is nitrogen, such as acetonitrile or pyridine, is brought in contact with the ruthenium dimer complex. To the resulting solution, a compound of the formula B+Axe2x88x92 is added to precipitate out the chloride salt. For example, NH4PF6 or TlPF6 can be used as the salt for precipitating out NH4Cl or TlCl. Finally, a neutral electron donor ligand which possesses sterically encumbering substituents, such as tricyclohexylphosphine, is added to the solution, and the obtained complex catalysts are recovered. 
For preparing the catalyst of the present invention represented by formula (II), any neutral electron donor ligand that can coordinate to the central ruthenium atom in a bidentate fashion, for example bidentate ligands derived from phosphorus, nitrogen, arsenic or a combination of these (such as arphos) is used in the last step of the synthetic scheme. 
For preparing the catalyst on the present invention represented by formula (III), tridentate neutral donor ligands, such as tridentate ligands derived from phosphorus as well as nitrogen, are used in the last step of the synthetic scheme.
We have discovered two routes for synthesizing the complexes according to the invention, both of which result in practically quantitative yields. In both instances, the starting material is a ruthenium dimer complex represented by the formula [(X1)(X2)RuY2], such as an [(allyl)RuCl2]2 dimer complex wherein (allyl) is the 2,7 dimethyl-octadienediyl ligand. Those two synthetic schemes are further illustrated below with specific reagents. 
In the first route, Reaction Scheme A, the [(allyl)RuCl2]2 dimer complex is dissolved in THF and a stoichiometric amount of AgBF4, NH4PF6 or TlPF6 (four equivalents) is added to the stirring solution. After the precipitation of halide salt is completed, the solution is filtered through a short column of Celite(trademark) (2xc3x972 cm), and to the eluate the neutral electron donor ligand is added. The reaction is allowed to continue for two hours at ambient temperature, preferably under a blanket of nitrogen or any inert gas. At the end of this period, the contents are evacuated under reduced pressure, and the crude solid obtained in this manner is washed with copious amounts of cold pentane. The complexes obtained this way are pure for most practical purposes and usually do not require additional purification procedures. 
In the second route, Reaction Scheme B which is a one-step synthesis, the [(allyl)RuCl2]2 dimer complex is dissolved in an appropriate solvent, and a stoichiometric amount of AgBF4, NH4PF6 or TlPF6 (four equivalents) along with a stoichiometric quantity of the neutral electron donor ligand (also four equivalents) are added all at the same time. The reaction is allowed to proceed at ambient temperature, preferably under a blanket of nitrogen or any inert gas for three hours, and at the end of this period the entire contents are filtered through a short column of Celite(trademark) (2xc3x972 cm). The filtrate is evacuated under reduced pressure and the crude product collected is washed (3xc3x9710 mL) with cold pentane. The catalyst obtained this way is also pure for all practical purposes.
The catalysts of the invention are stable in the presence of a variety of functional groups including hydroxyl, thiol, ketone, aldehyde, ester, ether, amine, imine, amide, nitro, carboxylic acid, disulfide, carbonate, isocyanate, carbodiimide, carboalkoxy, and halogen. Hence, the starting materials and products of the reactions described below may contain any one or more of these functional groups without poisoning the catalyst. Furthermore, these catalysts are stable in aqueous, organic, or protic solvents, for example aromatic hydrocarbons, chlorinated hydrocarbons, ethers, aliphatic hydrocarbons, alcohols, water, or mixtures of the above. Therefore, the preparations of the catalysts may be carried out in one or more of these solvents without poisoning the catalyst product.
The complex catalysts of the invention are effective in initiating metathesis reactions in olefins. In particular, they are highly effective catalysts for the polymerization of olefins, which may be cyclic or acyclic olefins, the latter having at least two double bonds in a molecule. The cyclic olefins may be monocyclic, bicyclic or tricyclic, and include ring-strained cyclic olefins such as norbornene and derivatives thereor, dicyclopendadiene and derivatives thereof, and trans-cyclooctadiene and derivatives thereof, as well as unstrained cyclic olefins including those having at least five carbon atoms in the ring such as cyclopentene, cycloheptene, trans-cyclooctene, etc. These olefins, whether cyclic or acyclic, may optionally have up to three substituents. Examples of such substituents are an alkyl group or a functional moiety such as hydroxyl, nitro, a halogen, thiol, thioether, ketone, aldehyde, ester, ether, amine, imine, amide, carboxylic acid, disulfide, carbonate, isocyanate, carbodiimide, carboalkoxy, and carbamate.
In a preferred embodiment of the invention, the complexes of the invention can initiate the ring opening metathesis polymerization (ROMP) of a cyclo-olefin monomer like NB without the use of any co-catalyst (such as a diazo alkyl compound). The ROMP of NB is practically instantaneous, and monomer to catalyst ratios of 10,000:1 effortlessly produce quantitative conversions. Even at ratios of up to 50,000:1 which were tried, the conversion had been extremely promising. For DCPD, however, we have discovered that it is critical for the catalyst to have at least one N donor ligand to exhibit robustness in the presence of the diazo alkyl compound. Therefore, a co-catalyst such as a diazo alkyl compound is required for the polymerization of DCPD.
Most of the complexes of the invention can be used in the presence of air. However, when oxygen and moisture are excluded from the system the activity demonstrated by these catalysts increases.
In a preferred embodiment of the invention, in-depth examination in our laboratory has revealed that when highly sterically encumbering ligands like tricyclohexylphosphine or triisopropylphosphine were coordinated to the ruthenium central atom, the catalyst could perform independently as an effective source for initiating the ROMP of NB without the use of a diazo alkyl compound. The rate of polymerization was found to be directly proportional to the magnitude of the steric bulk on the ligand, with tricyclohexylphosphine groups exhibiting the fastest rates. Furthermore, cycloalkyls or secondary alkyl substituents demonstrated a higher reactivity than aryl substituents for the same donor molecule. The polymerizations were very rapid when phosphorus was the donor molecule, followed by nitrogen and arsenic with the same substituents. In the investigations of bidentate and tridentate donor ligands it was also discovered that the phosphines were the most reactive catalysts, followed by amines and arsines.